The present invention relates to a coating method and a coating apparatus with which a coating solution fed through a supply port from the outside is distributed to a coating solution reservoir chamber and the distributed coating solution is fed through a slit toward the side of a internal circumferential surface and is coated on the outer circumferential surface of a cylindrical base member moving relative to the coating apparatus, in particular, to a coating method and a coating apparatus with which a coating solution is coated uniformly on an external circumferential surface of a cylindrical base material having a continuous surface formed endlessly. This type of the coating apparatus is preferably used as the coating apparatus to coat a coating solution containing a light sensitive material at the time of manufacturing a photoreceptor drum for use in an electrophotographic type image forming apparatus.
With regard to a method of coating a thin layer uniformly on an external circumferential surface of a cylindrical base material, there have been studied various methods such as a spray coating method, a dip coating method, a blade coating method and a roll coating method. In particular, for the coating of a uniform and thin layer such as that on an electrophotographic photoreceptor drum, development of a coating apparatus which is excellent to be manufactured is now studied. However, in a conventional coating apparatus an coating method for a cylindrical base material having a endlessly formed continuous surface, there are week points that an even coating layer could not be obtained and a productivity is not so good.
In the spray coating method, before a drop of coating solution jetted out of a spray gun reaches the external circumferential surface of a cylindrical base material having a continuous surface formed endlessly, a solvent evaporates, and thereby solid body concentration in the drop of a coating solution rises and viscosity of the coating solution is raised accordingly. Therefore, when the drop of a coating solution reaches the surface, the drop of a coating solution does not spread on the surface, or a particle dried and solidified sticks to the surface, resulting in an impossibility of obtaining those having coated surfaces which are excellent in smoothness. Further, the rate of reaching of a drop of a coating solution to a cylindrical base material having a continuous surface is not 100% resulting in a loss of a coating solution, and it is very difficult to control a layer thickness because uniformity is partially poor. In addition, in the case of a highly polymerized solution, cobweb formation is sometimes caused, and there accordingly are restrictions for solvents and resins to be used.
In the blade coating method and roll coating method, a blade or a roll is arranged in the longitudinal direction of a cylindrical base material, for example, so that the cylindrical base material is rotated for coating, and after the cylindrical base material makes one turn, the blade or the roll is retreated. However, when the blade or the roll is retreated, viscosity of a coating solution makes a part of a coated layer to be thicker than other portions, which is a weak point that a uniform layer can not be obtained.
In the dip coating method, smoothness on the surface of a coating solution and poor uniformity of a coated layer as stated above are improved.
However, control of a thickness of a coated layer depends on physical properties of a coating solution such as viscosity, surface tension, density and temperature as well as a coating speed, and therefore, adjustment of physical properties of a coating solution is very important. Further, there are further disadvantages that a coating speed is low and an amount of solution that is not less than a certain level is required for filling a tank for a coating solution. Further weak point is that components of lower layers melt out in the case of multi-layer coating and the tank for a coating solution is easily contaminated accordingly.
Under the background stated above, a ring-shaped amount regulating-type coating apparatus as described in Japanese Patent Publication Open to Public Inspection No. 189061/1983 and No. 60-95440 (hereinafter referred to as Japanese Patent O.P.I Publication) was developed. In this coating apparatus, a coating solution fed through a supply port from the outside is distributed to a ring-shaped coating solution reservoir chamber and the distributed coating solution is fed through a slit toward a internal circumferential surface and is coated uniformly on an external circumferential surface of a cylindrical base material having a continuous surface which is formed endlessly and is moved relative to the coating apparatus. In particular, the extrusion type coater described in a printed copy of the latter Japanese Patent O.P.I Publication is only one capable of coating a high viscosity coating solution onto a cylindrical base member.
This extrusion type coater directly extrudes a coating solution fed into a coating solution distributing chamber (a coating solution reservoir chamber) through a coating solution distributing silt to a coating solution flow-out port so as to form a bead between the cylindrical base member and the coating solution flow-out port, thereby coating continuously.
This extrusion type coater can adjust finely an amount of the coating solution fed through the slit and can coat with a small amount of the coating solution. As a result, the coating solution is not soiled, and the coating capable of being a high productivity and controlling the layer thickness easily can be realized.
However, even in the above coating apparatus, there is a problem that fluctuation in the thickness takes place so as to cause coating irregularities. In particular, in the extrusion type coater described in the latter Japanese Patent O.P.I Publication, the problem that the bead is discontinued occurs when a high viscosity coating solution is used. As result of energetic study, the present inventor found that the above problem has a close relation with the movement of the coating solution in the slit, that is, the absolute pressure in the coating solution distributing chamber.
The problem to be solved by the present invention is to make the movement of the coating solution in the slit stable and to reduce the coating irregularities. Further, the objective of the present invention is to conduct coating uniformly stably without causing coating failure and coating irregularities and without a long stay of a solution or a vapor in the coating solution distributing chamber.
The above problem can be solved by the following coating method:
A coating method of coating an outer circumferential surface of a cylindrical base with a coater having a supply port, a coating solution chamber, and a slit communicating with the coating solution chamber, the slit being provided around an inner circumferential surface of the coater, comprising steps of:
feeding a coating solution from the supply port to the coating solution chamber so that the coating solution is discharged to the slit;
adjusting an absolute pressure P in the coating solution chamber so as to satisfy the following formula:
3xc3x97104xe2x89xa6Pxe2x89xa63xc3x97106 (mmH2O)
and
relatively moving the cylindrical base through a hole formed by the inner circumferential surface of the coater so that an outer circumferential surface of the cylindrical base is uniformely coated with the coating solution flowing out from the slit.
The above problem can be solved by the following coating apparatus:
A coating apparatus to coat a coating solution on an outer circumferential surface of a cylindrical base, comprising:
a coater body provided with
a supply port,
a coating solution chamber,
an inner circumferential surface forming a hole through which the cylindrical base passes the coater body,
a slit provided around the inner circumferential surface, wherein the supply port, the coating solution chamber, and the slit are communicated so as to flow the coating solution;
a feeding means for feeding the coating solution from the supply port into the coating solution chamber so that an absolute pressure P in the coating solution chamber is adjusted to satisfy the following formula and the coating solution is distributed from the coating solution chamber to the slit:
3xc3x97104xe2x89xa6Pxe2x89xa63xc3x97106 (mmH2O)
a moving means for relatively moving the cylindrical base so as to pass through the hole so that an outer circumferential surface of the cylindrical base is coated with the coating solution flowing out from the slit.
Further, the above problem can be solved by the following coating method as the more prefereable method:
In a coating method in which a coating solution fed through a supply port from the outside is distributed to a ring-shaped coating solution reservoir chamber and the distributed coating solution is fed through a slit toward an inner circumferential surface and is coated on the outer circumferential surface of a cylindrical base member moving relative to a coater, the coating method of the present invention is characterized in that the absolute pressure in the coating solution reservoir chamber satisfy the following formula:
3xc3x97104xe2x89xa6P less than 3xc3x97106 (mmH2O)
In the coating method of the present invention, since the absolute pressure in the solution reservoir chamber satisfy the following formula: 3xc3x97104 xe2x89xa6P less than 3xc3x97106 (mmH2O), the movement of a high viscosity coating solution in the slit becomes stable. Whereby fluctuation in the layer thickness of the coating solution coated on the cylindrical base member can be refrained and coating irregularities can be reduced.
In a coating apparatus comprising a supply port through which a coating solution is fed from the outside, a ring-shaped coating solution reservoir chamber to distribute the coating solution fed through the supply port in the form of a ring, and a ring-shaped slit to feed the coating solution from the coating solution reservoir chamber toward an inner circumferential surface, the coating solution fed through the slit is coated on an outer circumferential surface of the cylindrical base member moving relative to the coating apparatus, the coating apparatus of the present invention is characterized in that the absolute pressure in the solution reservoir chamber satisfies the following formula:
3xc3x97104xe2x89xa6Pxe2x89xa63xc3x97106 (mmH2O)
In the present invention, xe2x80x9cabsolute pressurexe2x80x9d means a gage pressure.
Further, in a coating method in which a coating solution fed through a supply port from the outside is distributed to a ring-shaped coating solution reservoir chamber and the distributed coating solution is fed through a slit toward so as to be coated on the outer circumferential surface of a cylindrical base member, the coating method of the present invention is characterized in that the coating solution fed through the supply port is fed to the bottom portion in the coating solution reservoir chamber having a cross sectional shape formed by a curve, and the coating solution in the coating solution reservoir chamber is pressed to be fed through the slit toward an inner circumferential surface and is coated on the outer circumferential surface of the cylindrical base member moving relative to the coater.
Further, in a coating apparatus surrounding around a cylindrical base member moving in its longitudinal direction and comprising therein a ring-shaped coating solution reservoir chamber, a supply port through which a coating solution is fed from the outside to the coating solution reservoir chamber and a slit to form a conduit on an inner section from the coating solution reservoir chamber, the coating apparatus of the present invention is characterized in that the inlet section of the supply port is located at a bottom portion in the coating solution reservoir chamber and the cross section of the coating solution reservoir chamber is formed by a curve.
The coating method used in the present invention can be applicable to a simultaneous multi-layer coating method and a successive multi-layer coating depicted in FIG. 1 and FIG. 2 in the printed copy of Japanese Patent O.P.I Publication No. 60-95440.